While it is up to the feed manufacturers to insure the quality of the feed leaving the mill, it is up to you to make sure it is stored properly once you get it home. It is never a good idea to buy more sweet feed than you can use in one month or more pelleted feed than you can use in three months. During the summer you may want to consider purchasing even more frequently to reduce the risk of spoilage. Good storagefacilities will reduce any loss of nutrient value or contamination to your feed. Your storage place should meet several requirements. 

1. It should allow good ventilation of the feed and remain at a fairly constant cool temperature  with low humidity. As temperature and humidity increase so do problems with mold and  insects.
2. Feed should be protected from direct sunlight, moisture, mice, birds and other pests, and perhaps most importantly from horses and other livestock.
3. The storage area should be clean and in a convenient location.

Your storage facility will vary depending on the number of horses you are feeding. Clean metal garbage cans work well if you have only a few horses, however if you have a number of animals you may want to invest in a feed bunk or galvanized metal bulk storage bin. A good bin will reduce your costs and protect the feed from pests and spoilage.